Rigging the PW2000
"A harness problem," he says, "typically shows up as an intermittent indication. If you have a hard fault or one which is always there, there is less of a chance that the problem is harness related."
Clements continues, "The Boeing recommended approach to component fault messages is to write down, or record your fault message from the EPCS, check the source of the message, perform an erase procedure to the engine, and then apply alternate EEC power to see if you have duplicated the problem. If the fault is still there, it is considered a "hard" fault, which is typically inside of the component in question. If it is not a "hard" fault and the item didn't come back, it is considered an "intermittent" fault and you need to take the time to go through the engine and move harnesses around, re-installing plugs, etc. to see if you can duplicate the problem. If you can't, it may have just been a nuisance fault in the computer system — a high-tech hiccup."
"The EICAS system can sometimes behave like your laptop computer, where just re-booting it will make the error go away and never come back. But for safety's sake, it's important to investigate the potential source of any problem to be sure there is nothing wrong," he explains. "Mechanics should always consult the Boeing 757 Fault Isolation Manual (FIM) when troubleshooting component fault messages."
To rig the 2.5 actuator, you first need to verify that you are getting full travel of the 2.5 bleed valve with full travel of the actuator. To do this, you first remove the hydraulic lines from the actuator and stroke the actuator to remove any fluid. Then, move the actuator through its full travel by hand while observing the movement of the 2.5 valve.
Before adjusting the rigging of the 2.5 bleed, you first have to check for excessive play in the linkage. To do this, you insert a locally fabricated tool into the 2.5 bleed ring to hold it into the full open position. With this accomplished, you then move the actuator back and forth and make sure that you have less than .250 inch movement in the linkage. Anything over .250 of movement, and you have to tear down the assembly and linkage and rework it. You should check the maintenance manual for reduced interval inspection criteria in relation to linkage wear.
With this established, you can now check the rigging on the actuator. You do this by placing a depth micrometer onto the top surface of the LVDT and zeroing it out. Next, you move your actuator all the way to the forward position. You then move your depth micrometer to the new location and it should read between 2.6 and 2.66 inches. If you don't get this reading, the actuator may be unserviceable. In this case the actuator must be removed and replaced. Once the travel is within these dimensions, proceed to rig the actuator to the bleed linkage according to the manual.
The objective of the rigging is to make adjustments so that when the actuator is in the EEC commanded closed position, the bleed ring is fully closed. To rig it properly, the manual describes a procedure whereby you apply a load of 75 lbf to the rod end. This pressure can be held on the rod end with a special PWA fixture or other acceptable means. With the actuator rod end loaded to 75 lbf, the rigging pin is inserted, and the linkage adjuster is backed out until it bumps against the rig pin. You then can move the adjuster up to 1/2 turn forward so it lines up with the clevis bolt. When you are done performing the rigging procedure, you were instructed in the original procedure to check, using hydraulic pressure on the actuator, the stroke of the actuator and measure at the LVDT to make sure that you are still getting the 2.6 to 2.66 dimension.
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